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Shallow and Deep States of Beryllium Acceptor in GaN: Why Photoluminescence Experiments Do Not Reveal Small Polarons for Defects in Semiconductors

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Physical Review Letters 2021年第2期126卷 027401-027401页

作者： D. O. Demchenko M. Vorobiov O. Andrieiev T. H. Myers M. A. Reshchikov Department of Physics Virginia Commonwealth University Richmond Virginia 23220 USA Materials Science Engineering and Commercialization Program Texas State University San Marcos Texas 78666 USA

Currently, only one shallow acceptor (Mg) has been discovered in GaN. Here, using photoluminescence (PL) measurements combined with hybrid density functional theory, we demonstrate that a shallow effective-mass state also exists for the BeGa acceptor. A PL band with a maximum at 3.38 eV reveals a shallow BeGa acceptor level at 113±5 meV above the valence band, which is the lowest value among any dopants in GaN reported to date. Calculations suggest that the BeGa is a dual-nature acceptor with the “bright” shallow state responsible for the 3.38 eV PL band, and the “dark,” strongly localized small polaronic state with a significantly lower hole capture efficiency.

关键词： Defects Electronic structure Doped semiconductors Semiconductor compounds Density functional calculations Photoluminescence

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Synthesis and characterization of hydrotalcite like compound via a facile solid state method

Synthesis and characterization of hydrotalcite like compound...

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作者： Fahami, Abbas Beall, Gary W. Materials Science Engineering and Commercialization Program Texas State University San MarcosTX78666 United States Department of Chemistry and Biochemistry Texas State University San MarcosTX78666 United States Physics Department Faculty of Science King Abdulaziz University Jeddah21589 Saudi Arabia

Carbonate intercalated Mg-Al layered double hydroxides (Mg-Al-CO3-LDH) were successfully produced by mechanical alloying process using different starting raw chemicals. Two distinct chemical reactions were activated at different milling times. The samples were characterized by Xray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Results revealed that the structural characteristics of Mg-Al-CO3-LDH such as lattice parameters, unit cell volume, and the interlayer spacing were affected strongly by milling time. Based on the XRD data, the formation rate of pure Hydrotalcite (HT) was strongly influenced by the chemical composition of raw materials. Electron microscopic observation displayed that the final product had a platelet-like structure with an average particle size of 20-100 nm. Therefore, the synthesis of Mg-Al-CO3-LDH via a cost-effective solid-state method owing to simplicity and reproducibility can be a promising candidate especially for use in biomaterials and catalyst industries. © 2016 materials Research Society.

关键词： Mechanical alloying

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Effects of surface treatment of alumina nanofibers on mechanical and thermal properties of polyester e-glass composites

Effects of surface treatment of alumina nanofibers on mechan...

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International SAMPE Conference and Exhibition 2020

作者： Kallagunta, Harish S.P. Tate, Jitendra S. Beall, Gary W. Panta, Subash Beldeque, Maria Akanda, Muzaffer Islam, Rafiqul Texas State University 601 University Drive San MarcosTX78666 United States Materials Science Engineering and Commercialization Program Texas State University United States Ingram School of Engineering Texas State University United States Department of Chemistry and Biochemistry Texas State University United States

Dispersibility of the nanoparticles in the matrix is one of the critical factors influencing various properties of nanocomposites. To address the issue of agglomeration in nanocomposites and negate the effects on properties, surface treatment of nanoparticles is seen as the viable solution. This study is focused on the influence of alumina nanofiber (NafenTM) loadings and surface treatment of the alumina nanofibers (NafenTM) on thermal and mechanical properties of polyester/E-Glass composites. Loading levels of 0.25wt%, 0.5wt%,0.75wt% and 1wt% for both untreated alumina nanofibers and silane surface treated alumina nanofibers were selected and are dispersed into polyester resin using three-roll mill. Transmission Electron Microscopy (TEM) revealed that at higher loading levels, the alumina nanofibers tend to agglomerate. Thermogravimetric analysis was performed on the unreinforced nanocomposite coupons and the increase in thermal degradation behavior with addition of nanoparticles. Silane treatment of alumina nanofibers have seemed to improve the lower onset degradation temperature. Static mechanical studies were performed. The mechanical behavior improved with addition of alumina nanofibers. Major improvement in properties is observed at 0.25wt% and 1wt% silane treated alumina nanofiber modified glass polymer composites. © 2020 Soc. for the Advancement of Material and Process engineering. All rights reserved.

关键词： Surface treatment

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MECHANICAL PROPERTIES OF RE-EXTRUDED SrFe12O19(OP-71)/PA12 FILAMENTS VIA TWIN-SCREW EXTRUSION FOR FUSED FILAMENT FABRICATION 8

MECHANICAL PROPERTIES OF RE-EXTRUDED SrFe12O19(OP-71)/PA12 F...

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8th Annual Composites and Advanced materials Expo, CAMX 2021

作者： Belduque, Camila Ahmed, Tanjina Geerts, Wilhelmus Panta, Subash Thramann, Harrison Omer, Liam Tate, Jitendra Ingram School of Engineering Texas State University 601 University Drive San MarcosTX78666 United States Materials Science Engineering and Commercialization Program Texas State University 601 University Drive San MarcosTX78666 United States Department of Physics Texas State University 601 University Drive San MarcosTX78666 United States

ISBN: (纸本)9781934551400

The most employed permanent and soft magnetic materials, such as Strontium Ferrite (SrFe12O19) is attractive to be dispersed in polymers such as polyamides or ABS to obtain new composites in the additive manufacturing industry. Specifically fused filament fabrication offers a low cost, accessible, and environmentally friendly process. Products such as MRI devices, robots for drug delivery and automotive parts are some of the potential applications that can be developed given a highly filled matrix with homogeneously dispersed magnetic fillers. Twin-screw extrusion is recognized as one of the efficient methods to obtain uniform dispersion of magnetic fillers. Uniform dispersion is key factor in enhancement in mechanical and magnetic properties. In this project, 50wt% SrFe12O19/Pa12 magnetic powder was dispersed in PA12 matrix using twin-screw extrusion. Mechanical properties are analyzed in both extruded and re-extruded composites using MTS 810 following ASTM standards. Double pass extruded SrFe12O19/Pa12 (OP-71/PA12D) samples exhibited unprecedented tensile and flexural strength increases compared to both neat PA12 and single pass extruded SrFe12O19/Pa12 (OP-71/PA12). Copyright 2021. Used by CAMX – The Composites and Advanced materials Expo

关键词： 3D printers

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EFFECT OF BALL MILLING ON THE MAGNETIC PERFORMANCE OF STRONTIUM FERRITE (SrFe12O19) POWDERS

EFFECT OF BALL MILLING ON THE MAGNETIC PERFORMANCE OF STRONT...

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SAMPE 2024 Conference and Exhibition

作者： Arigbabowo, Oluwasola K. Hassan, Mehadi Asadollahnejad, Azin Islam, Md Shafikul Price, Holt Geerts, Wilhelmus J. Tate, Jitendra Materials Science Engineering and Commercialization Program Texas State University 601 University Drive San MarcosTX78666 United States Ingram School of Engineering Texas State University 601 University Drive San MarcosTX78666 United States Department of Physics Texas State University 601 University Drive San MarcosTX78666 United States

ISBN: (纸本)9781934551455

The primary advantage of the high energy ball milling (HEBM) process is its ability to synthesize a homogeneous mixture with submicron (up to nanoscale) particle size. This approach is a viable process for particle size reduction and grain refinement of magnetic powders, which affects their domain structure and by extension the resulting magnetic properties. In this research, we designed a 9-ball milling experiment by keeping the rotational speed constant at 300rpm and varying the ball-to-powder ratio of 5:1, 8:1, and 10:1 for 6hrs, 10hrs, and 14hrs milling times. The strontium ferrite magnetic powders subjected to HEBM were analyzed for crystallite size and behavior via XRD, particle size reduction via SEM/ImageJ software/originLabPro, and magnetic performance via powder-based VSM measurement. The magnetic performance of the ball-milled strontium ferrite powders shows a good combination of appreciable increment in the S-values (a ratio of the remanence to saturation magnetization) and a considerable decline in coercivity ( © 2024 Soc. for the Advancement of Material and Process engineering. All rights reserved.

关键词： Grain refinement

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MAGNETIC PROPERTIES EVALUATION OF POLYAMIDE 4.6 BONDED MAGNETIC COMPOSITE

MAGNETIC PROPERTIES EVALUATION OF POLYAMIDE 4.6 BONDED MAGNE...

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SAMPE 2024 Conference and Exhibition

作者： Karkhanis, Pratik Arigbabowo, Oluwasola K. Gonzalez, Aaron J. Inamdar, Shreyas Ahmed, Tanvir Herrera, Andres Geerts, Wilhelmus J. Tate, Jitendra S. Ingram School of Engineering Texas State University 601 University Drive San MarcosTX78666 United States Materials Science Engineering and Commercialization Program Texas State University 601 University Drive San MarcosTX78666 United States Department of Physics Texas State University 601 University Drive San MarcosTX78666 United States

ISBN: (纸本)9781934551455

Bonded magnetic composites combine the cost-effectiveness, low density, and manufacturing flexibility of conventional polymer binders with the unique magnetic characteristics of magnetic powders/fillers to form multifunctional magneto polymeric composites that offer superior properties to conventional sintered magnets. In this study, a co-rotating twin screw extruder was used to fabricate 20 and 40 wt.% strontium ferrite/polyamide 4.6 bonded magnetic composites viable for fused filament fabrication 3D printing. The characterization conducted on the bonded magnetic composites was scanning electron microscopy, simultaneous differential thermogravimetry, and vibrating sample magnetometry. The microstructure of the bonded composite exhibited a uniform platelet morphology of the strontium ferrite magnetic particles. There was no observable depreciation in the melting transitions, which suggests a thermally resistant magnetic composite. An appreciable increment in % crystallinity of 13 and 20% for 20wt.% and 40wt.% strontium ferrites bonded magnets were observed. This is attributable to the heterogeneous nucleation phenomenon, where the metal powders act as nucleation sites for increased crystalline domains. The bonded composite exhibited significant magnetic anisotropy, with the remanence (Mr), which is the most important property for magnetic application significantly increasing to 49.8% along the easy direction in comparison to the hard axis. This suggests the viability of the fabricated bonded composites in viable in producing anisotropic bonded magnetic devices, which are considered to exhibit stronger magnetic properties. © 2024 Soc. for the Advancement of Material and Process engineering. All rights reserved.

关键词： Magnetic anisotropy

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HAADF-STEM Study of Filament Material in Hot Filament CVD Diamond Films

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Microscopy and Microanalysis 2019年第S2期25卷 1788-1789页

作者： Jonathan Anderson Raju Ahmed Anwar Siddique Edwin L. Piner Materials Science Engineering and Commercialization Program Texas State University San Marcos Texas United States. Department of Physics Texas State University San Marcos Texas United States.

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HIGH-PERFORMANCE THERMOPLASTIC-BASED MAGNETIC COMPOSITES

HIGH-PERFORMANCE THERMOPLASTIC-BASED MAGNETIC COMPOSITES

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SAMPE 2023 Conference and Exhibition

作者： Arigbabowo, Oluwasola K. Tate, Jitendra Geerts, Wilhelmus J. Texas State University Materials Science Engineering and Commercialization Program 601 University Drive San MarcosTX78666 United States Ingram School of Engineering Texas State University 601 University Drive San MarcosTX78666 United States Department of Physics Texas State University 601 University Drive San MarcosTX78666 United States

ISBN: (纸本)9781934551431

Magnetic polymer-based composites combine the cost-effectiveness, low density, and manufacturing flexibility of conventional polymers with the unique characteristics of magnetic powders/fillers to form multifunctional magneto polymeric composites that offer superior properties to conventional materials. At higher temperatures, magnetic properties change significantly and the particles within the magnetic powders experience sporadic motion due to the heat which causes misalignment of the magnetic domains, leading to a decrease in magnetism. Due to these adverse temperature effects, high-performance polymers such as polyetheretherketone (PEEK), polyetherimide (PEI) or other high-temperature thermoplastics have been considered suitable matrix for the magnetic fillers, thereby creating a much wider usage for magneto polymeric composite in applications that requires higher temperature (typically above 175 oC). Thus, this review discusses the fabrication processes-injection molding, fused filament fabrication;magnetic performance, and applications of high-performance thermoplastic-based magnetic composites that can be viable for stringent engineering devices such as sensors, actuators, motors, and generators. © 2023 Soc. for the Advancement of Material and Process engineering. All rights reserved.

关键词： Fabrication

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Growth, optimization and high-temperature performance of GeO2/Ga2O3 MOSCAPs

SSRN

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SSRN 2024年

作者： Manikanthababu, N. Karmakar, Subrata Shiam, Ishtiaq Firoz Emu, Injamamul Hoque Haque, Ariful Droopad, Ravi Electrical Engineering Ingram School of Engineering Texas State University San MarcosTX78666 United States Materials Science Engineering & Commercialization Program Texas State University San MarcosTX78666 United States

In this study, GeO2 thinfilms were grown by pulsed laser deposition (PLD) technique on β-Ga2O3, (―201) single crystal substrates to fabricate metal-oxide-semiconductor capacitors (MOSCAPs), and test these devices at high temperatures. The GeO2 thinfilms with bandgap of 5.11 eV are amorphous in nature, confirmed by X-ray diffraction, and the X-ray photoelectron spectroscopy (XPS) confirms the formation of GeO2. The Ge 3d deconvoluted peak at 32.4 eV confirms the GeO2 bonding, with an additional peak found at 30.9 eV resembling a small portion of GeO2-x. The Au/GeO2/Ga2O3 MOSCAPs were fabricated to test the high-temperature performance up to 300 oC. The I–V graphs showed an increase in the reverse leakage current by 3.9×104 A (nearly four orders of magnitude) as the temperature raised from room temperature (RT) to 300 oC. Since the GeO2-x presence, the current conduction mechanism of Poole-Frenkel emission was utilized to get the trap level of 0.8 V (below the conduction band of GeO2) with an activation energy of 0.55 eV. C–V measurements also show a significant contribution of defects in the flat-band voltage shift and the change of the slopes. This indicates an increase in the oxide and interface-trapped charges. The density of oxide-trapped charges (DO) increased from 3.9×1012 cm-2 to 1.3×1013 cm-2, as the temperature reached 300 oC. Similarly, the density of interface-trapped charges (DI) increased from 3.4×1012 cm-2 at RT to 1.1×1013 cm-2 at 300 oC. © 2024, The Authors. All rights reserved.

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N- and P-Type Doping of Diamonds: A Review

SSRN

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SSRN 2024年

作者： Sultana, Maria Karmakar, Subrata Haque, Ariful Ingram School of Engineering Texas State University San MarcosTX78666 United States Materials Science Engineering & Commercialization Program Texas State University San MarcosTX78666 United States

Diamond has been one of the most investigated ultrawide bandgap (UWBG) semiconductors for optoelectronics, superconductors, energy, and quantum applications for almost half of a century owing to its unique properties. Diamonds' intrinsic features- a large bandgap (5.47 eV), an extremely high breakdown voltage (10 MV/cm), the highest thermal conductivity (2200 W/m-K), and very high radiation-tolerance, make them promising for high-power, high-frequency devices suitable for high-temperature and extreme radiation environments. Since the demand for high-speed consumer electronics with large power and faster data handling capacity is rising at an unprecedented rate in the post-COVID era, diamonds' excellent mobility of electrons and holes (4500 and 3800 cm2/V-s) make them ideal for servers and systems. To materialize these multipurpose devices with higher efficiency and endurance than Si and SiC-based technologies, diamonds with good p- and n-type conductivity are needed. Therefore, nearly several decades-long efforts have been devoted to understanding and controlling the carrier conductivities in diamonds. Furthermore, diamonds' color centers' remarkable application as the qubit for next-generation quantum computers has also sparked interest in investigating diamond point defects at the quantum level. Hence, it is necessary to comprehensively study the fabrication, doping, and applications in semiconducting and quantum devices to stay relevant to the diamond revolution and thus advance this flourishing field. Therefore, this review article summarizes the current status and breakthroughs in diamond doping and devices fabricated using doped diamonds to provide an overview of the challenges and successes in using this highly promising UWBG material in electronic, superconducting, and quantum applications. © 2024, The Authors. All rights reserved.

关键词： Diamonds

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